The present invention relates to a new and improved construction of a twin-wire papermaking machine.
Generally speaking, the twin-wire papermaking machine of the present development is of the type comprising a headbox for forming a first fiber ply and contains a pre-dewatering path located at a first wire and which is arranged after or downstream of the headbox. This pre-dewatering path serves for dewatering the fiber ply essentially in a downward direction. Arranged downstream of the first wire is a common path formed by the first wire and a second wire and serving for dewatering the fiber ply essentially in an upward direction.
The twin-wire papermaking machine of the aforementioned type is known to the art from U.S. Pat. No. 4,176,005, granted Nov. 27, 1979. In order to fabricate at such type of papermaking machine paper composed of a number of layers or plies, it is known for instance to use a multiple headbox which contains a nozzle channel subdivided by intermediate or partition walls into partial channels or sub-passages. Through such partial channels different types of stock suspensions are guided separately from one another almost immediately up to the region of the headbox outlet gap or slice and then are almost simultaneously deposited upon the first wire. For the same purpose it is also known to provide a second headbox arranged following the first headbox and before the pre-dewatering path. By means of the second headbox there is deposited one or a number of additional fiber layers or plies upon the single or multi-ply fiber web which is already located upon the first wire and which has been formed by the first headbox.
With the state-of-the-art constructions it is necessary during the fabrication of multi-ply paper composed of a plurality of fiber layers or plies, to always dewater, for instance, the uppermost ply through the already formed ply or plies which are located for instance therebelow, and hence, it is necessary to overcome the prevailing dewatering resistance. This requires a relatively long pre-dewatering path with correspondingly longer dewatering times. Additionally, fibers can tend to again deflocculate, so that the formation of the fibers in the already formed layer or ply is impaired.